1. Field of the Invention
This invention relates generally to seating and more particularly to office type swivel chairs capable of adjustment of the seat tilt or inclination angle and the seat back angle.
2. Related History
Various desk or work station chairs having a seat, a seat back and possibly arm rests together with a support mechanism which interconnected at least the chair seat to a vertical post have been generally characterized as "office" chairs. The post usually included, at its base, a spider having radially projecting horizontal legs with depending casters for rolling contact with a floor support surface. Adjustment of the seat elevation was achieved through adjustment of the post height or the position of the seat support mechanism relative to the post. The seat support mechanisms often included a fixed pivot for adjustably varying the angle of the seat back relative to the seat.
Numerous seat support mechanisms which interconnected the seat with the support post and provided for adjustment of the horizontal inclination or tilt, of the seat have been suggested. Examples of some of these mechanisms are illustrated in U.S. Pat. No. 4,438,978, issued Mar. 27, 1984, U.S. Pat. No. 4,198,094, issued Apr. 15, 1980, U.S. Pat. No. 4,636,004, issued Jan. 13, 1987 and European Patent WO 81/00044, issued Jan. 22, 1981.
Unfortunately, a majority of the prior seat support mechanisms were designed without due consideration of the human anatomy. A principal drawback with respect to prior seat support mechanisms was that because the seat tilt axis was located rearwardly of the front edge of the seat, as the seat was tilted rearwardly, the front edge of the seat elevated, resulting in increased popliteal pressure in the areas of the peroneal and sciatic nerves. Such pressure generated a sensation of discomfort and strain rather than relaxation when the seat occupant tilted the seat back to obtain what would otherwise have been a more comfortable Seating position relative to the user's desk, workbench, terminal or other work station.
A further problem encountered with respect to prior seat and seat back support mechanisms, such as that illustrated in U.S. Pat. No. 4,062,587, was that the pivot point for seat back movement relative to the seat was often improperly selected and when a user adjusted the seat angle or tilted the seat rearwardly in synchronous movement seat support mechanisms which automatically adjusted the seat back angle when the seat was tilted, a noticeable change of the point of engagement between the seat back and the user's back resulted. Such dimensional change generated an undesirable translatory pressure along the user's spinal column.